The spelling of the word "prothero" follows the typical English spelling patterns. The first syllable is pronounced as "pro" with a long "o" sound, represented by the IPA symbol /oʊ/. The second syllable is pronounced as "ther" with a short "e" sound, represented by the IPA symbol /ɛ/. The final syllable is pronounced as "ro" with a long "o" sound, represented by the IPA symbol /oʊ/. Therefore, the IPA transcription of "prothero" is /ˈproʊ.ðə.roʊ/.